The invention is directed to a process for the preparation of a catalyst component for the polymerization of an olefin.
Catalyst components on a support for the preparation of polyolefins have a high activity and a high stereospecificity. These catalyst components are already known for a long time. Essential elements for the preparation of such catalyst components are a magnesium-containing support and a titanium compound attached thereto. For the polymerization of olefins also an alkylaluminum compound is needed as a cocatalyst.
High activity supported catalyst components are the most frequently used catalyst components for the polymerization of olefins, such as for instance propylene. By the high activity of the catalyst component a high yield of the polyolefin is obtained per weight percentage of the titanium compound in the catalyst component. Therefore it is no longer needed to remove the catalyst component from the polyolefin produced.
There are several methods to prepare the magnesium-containing support of the catalyst component. It is for instance possible to grind the magnesium-containing support, spraydrying it or to precipitate the magnesium-containing support. The magnesium-containing support can further be treated with a halogenating compound to prepare the magnesium-containing support. Several other methods to prepare magnesium-containing supports are for instance described by E. P. Moore (Jr.), Polypropylene Handbook, Hansen Publishers, 1996, p. 22.
A process for the preparation of such a supported catalyst component is for instance described in WO-A-96/32427. In this patent application a process for the preparation of a catalyst component for the polymerization of an olefin is described. In the preparation of the catalyst component a magnesium compound is contacted with a titanium compound wherein the magnesium compound is obtained by:
a) contacting metallic magnesium with an aromatic halide RX, where R is an aromatic group containing up to 20 carbon atoms and X is a halide, whereupon the resulting dissolved reaction product I is separated from the solid residual products and whereafter,
b) an alkoxy group or aryloxy group containing silane compound is added to the obtained reaction product I at a temperature of from xe2x88x9220 to 20xc2x0 C., whereupon the precipitate formed is purified to obtain reaction product II,
which reaction product II is subsequently, during a step c), is contacted with TiCl4, and the resulting product is purified to obtain the catalyst component.
Although the performance of this catalyst component is very good and this catalyst component already shows a high activity and selectivity, a more improved catalyst component is obtained by the process of the present invention wherein in step b) the silane compound and reaction product I are introduced simultaneously to a mixing device.
Here and hereafter xe2x80x9csimultaneous introductionxe2x80x9d means the introduction of reaction product I and the silane compound in such a way that the Mg/Si ratio does not substantially vary during the introduction of these compounds to the mixing device.
This process has the advantage that the morphology of the catalyst particles improves; especially for the larger catalyst particles. Here and hereafter xe2x80x98morphologyxe2x80x99 does not only refer to the shape of the catalyst particles, but also to the particle size distribution and the bulk density of the catalyst particles.
The polyolefin powder produced in the polymerization by using the catalyst component has the same morphology as the catalyst component; this is a known effect and is called the xe2x80x9creplica effectxe2x80x9d (S. van der Ven, Polypropylene and other Polyolefins, Elsevier 1990, p. 8-10). Using the catalyst compound prepared according to the process of the invention almost round polymer particles are obtained with a length/diameter ratio (1/d) smaller than 2 and a good powder flowability, while according to WO-A-96/32427 elongated polymer particles are obtained with a 1/d of more than 2.5.
During step b) the dissolved reaction product I, obtained after carrying out step a), is brought into contact with an alkoxy group or aryloxy group containing silane compound in such a way that reaction product I and the silane compound are introduced simultaneously to the mixing device.
The mixing device can have various forms; the mixing device can be a mixing device in which the silane compound is premixed with reaction product I, but the mixing device can also be the reactor in which reaction product II is formed.
The mixing device for simultaneously premixing the silane compound and reaction product I can be a mixing device in which the premixing takes place in a dynamic or a static way. Premixing in a dynamic way can take place by, for instance, mixing, stirring, shaking and by the use of ultrasonic waves. Premixing in a static way can take place in, for instance, a static mixer or in a tube wherein the silane compound and reaction product I are contacted. For the preparation of the catalyst component in big amounts both static and dynamic mixing can be used. Premixing in a dynamic way is preferably used when the catalyst component is prepared in small amounts. For the preparation of the catalyst component in big amounts preferably a static mixer is used for premixing the silane compound and reaction product I. Preferably, the silane compound and reaction product I are premixed before the mixture is introduced to the reactor wherein reaction product II is formed. In this way the catalyst component formed gives polymer particles with the best morphology.
Premixing is performed during 0.1 to 300 seconds; preferably during 1 to 50 seconds.
The temperature during the premixing is between 0 and 80xc2x0 C.; preferably between 10 and 50xc2x0 C.
The silane compound and reaction product I can be continuously or batch-wise introduced to the mixing device. Preferably, the silane compound and reaction product I are introduced continuously to the mixing device.
The formation of reaction product II normally takes place at a temperature between xe2x88x9220 and 100xc2x0 C.; preferably at a temperature of from 0 to 80xc2x0 C.
Preferably, reaction product I is contacted with the alkoxy group or aryloxy group containing silane compound in the presence of an inert hydrocarbon solvent such as the solvents mentioned further as dispersant in the discussion of step a). The solvent can be a solvent for the silane compound, a dispersant for reaction product I or be present in the reactor wherein reaction product II is collected. Combinations of these three possibilities are also possible.
Preferably, the reactor wherein reaction product II is obtained, is a stirred reactor.
The Si/Mg molar ratio during step b) may vary from 0.2 to 20. Preferably, the Si/Mg molar ratio is from 0.4 to 1.0.
The product from step b), reaction product II, is usually purified by rinsing with an inert hydrocarbon solvent and then used for the further preparation of the catalyst component in step c).
The following examples of alkoxy group or aryloxy group containing silane compounds may be mentioned: tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, tetraisobutoxysilane, tetraphenoxysilane, tetra(p-methylphenoxy)silane, tetrabenzyloxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, methyltriphenoxysilane, methyltriphenoxysilane, ethyltriethoxysilane, ethyltriisobutoxysilane, ethyltriphenoxysilane, butyltrimethoxysilane, butyltriethoxysilane, butyltributoxysilane, butyltriphenoxysilane, isobutyltriisobutoxysilane, vinyltriethyoxysilane, allyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, benzyltriphenoxysilane, methyltriallyloxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldiisopropyloxysilane, dimethyldibutoxysilane, dimethyldihexyloxysilane, dimethyldiphenoxysilane, diethyldiethoxysilane, diethyldiisobutoxysilane, diethyldiphenoxysilane, dibutyldiisopropyloxysilane, dibutyldibutoxysilane, dibutyldiphenoxysilane, diisobutyldiethoxysilane, diisobutyldiisobutoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, diphenyldibutoxysilane, dibenzyldiethoxysilane, divinyldiphenoxysilane, diallyldipropoxysilane, diphenyldiallyloxysilane and methylphenyldimethoxysilane.
Preferably use is made of tetraethoxysilane.
Step a) in the process for the preparation of the catalyst component of the invention is carried out by contacting metallic magnesium with an organic halide RX.
All forms of metallic magnesium may be used, but preferably use is made of finely divided metallic magnesium, for example magnesium powder. To obtain a fast reaction it is preferable to heat the magnesium under nitrogen prior to use. In the organic halide RX, R is an organic group preferably containing from 1 up to 20 carbon atoms and X preferably is chlorine or bromine.
Examples of the organic group R are methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, hexyl, octyl, phenyl, tolyl, xylyl, mesityl and benzyl. Combinations of two or more organic halides RX can also be used.
The magnesium and the organic halide RX can be reacted with each other without the use of a separate dispersant; the organic halide RX is then used in excess. The organic halide RX and the magnesium can also be brought into contact with one another in the presence of an inert dispersant. Examples of these dispersants are: aliphatic, alicyclic or aromatic dispersants containing from 4 up to 20 carbon atoms.
Preferably, in step a) also an ether is added to the reaction mixture. Examples of ethers are: diethyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, diisoamyl ether, diallyl ether, tetrahydrofuran and anisole. Dibutyl ether and/or diisoamyl ether are preferably used.
Preferably, an excess of chlorobenzene is used as the organic halide RX. Thus, the chlorobenzene serves as dispersant as well as organic halide RX. The organic halide/ether ratio acts upon the activity of the catalyst component. The chlorobenzene/dibutyl ether volume ratio may for example vary between 75:25 and 35:65.
When the chlorobenzene/dibutyl ether ratio decreases, the bulk density of the polyolefine powder prepared with the aid of the catalyst component becomes lower and when the chlorobenzene/dibutyl ether ratio increases, the amount of the dissolved reaction product I becomes lower. Consequently, the best results are obtained when the chlorobenzene/dibutyl ether volume ratio is between 70:30 and 50:50.
Small amounts of iodine and/or alkyl halides can be added to cause the reaction between the metallic magnesium and the organic halide RX to proceed at a higher rate. Examples of alkyl halides are butyl chloride, butyl bromide and 1,2-dibromoethane. When the organic halide RX is an alkyl halide, iodine and 1,2-dibromoethane are preferably used.
The reaction temperature for step a) normally is between 20 and 150xc2x0 C.; the reaction time between 0.5 and 20 hours.
After the reaction of step a) is completed, the dissolved reaction product I is separated from the solid residual products.
The further preparation of the catalyst component is carried out by contacting, during a step c), the purified reaction product II with TiCl4. 
Preferably an internal electron donor is also present during step c). Also mixtures of internal electron donors can be used. Examples of internal electron donors are carboxylic acids, carboxylic acid anhydrides, esters of carboxylic acids, halide carboxylic acids, ethers, ketones, amines, amides, nitrites, aldehydes, alcoholates, sulphonamides, thioethers, thioesters and other organic compounds containing a heteroatom, such as nitrogen, oxygen or phosphorus.
Examples of carboxylic acids are formic acid, acetic acid, propionic acid, butyric acid, isobutanoic acid, acrylic acid, methacrylic acid, maleic acid, fumaric acid, tartaric acid, cyclohexanoic monocarboxylic acid, cis-1,2-cyclohexanoic dicarboxylic acid, phenylcarboxylic acid, toluenecarboxylic acid, naphthalene carboxylic acid, phthalic acid, isophthalic acid, terephthalic acid and trimellitic acid. Anhydrides of the aforementioned carboxylic acids can be mentioned as examples of carboxylic acid anhydrides, such as acetic acid anhydride, butyric acid anhydride and methacrylic acid anhydride.
Examples of esters of carboxylic acids that can be mentioned are butyl formate, ethyl acetate, butyl acetate, ethyl acrylate, methyl methacrylate, isobutyl methacrylate, methylbenzoate, ethylbenzoate, methyl-p-toluate, ethyl-xcex1-naphthoate, monomethyl phthalate, dibutyl phthalate, diisobutyl phthalate, diallyl phthalate and diphenyl phthalate.
Examples of halide carboxylic acids that can be mentioned are the halides of the above mentioned carboxylic acids, such as acetyl chloride, acetyl bromide, propionyl chloride, butanoyl chloride, butanoyl iodide, benzoyl bromide, p-toluyl chloride and phthaloyl dichloride.
Examples of suitable ethers are diethyl ether, dibutyl ether, diisoamyl ether, anisole and ethylphenyl ether, 2,2-diisobutyl-1,3-dimethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 2-ethyl-2-butyl-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane and 9,9-bis(methoxymethyl)fluorene. Also, tri-ethers can be used.
Examples of other organic compounds containing a heteroatom are thiophenol, 2-methylthiophene, isopropyl mercaptan, diethylthioether, diphenylthioether, tetrahydrofuran, dioxane, dimethylether, diethylether, anisole, acetone, triphenylphosphine, triphenylphosphite, diethylphosphate and diphenylphosphate.
Preferably dibutyl phthalate is used as the internal electron donor.
The TiCl4/Mg molar ratio during step c) preferably is between 10 and 100. Most preferably, this ratio is between 10 and 50. The molar ratio of the internal electron donor, if used, relative to the magnesium in step c) may vary between 0.05 and 0.75. Preferably this molar ratio is between 0.1 and 0.4.
During step c) use is preferably made of an aliphatic or aromatic hydrocarbon compound as a solvent. Most preferably, the solvent is toluene or chlorobenzene.
The reaction temperature during step c) is preferably between 50 and 150xc2x0 C., most preferably between 60 and 120xc2x0 C. At higher or lower temperatures the activity of the catalyst component prepared according to the process of the invention becomes lower. The obtained reaction product in step c) is purified, usually with an inert hydrocarbon, to obtain the catalyst component of the invention.
The catalyst component of the invention is suitable for the preparation of polyolefines by polymerising one or more olefines in the presence of the catalyst component and a cocatalyst. The cocatalyst generally is an organometallic compound containing a metal from group 1, 2, 12 or 13 of the Periodic System of the Elements (Handbook of Chemistry and Physics, 70th Edition, CRC Press, 1989-1990). Preferably the cocatalyst is an organoaluminium compound. As the organoaluminium compound use is made of a compound having the formula RnAlX3-n, where X is a halogen atom, an alkoxy group or a hydrogen atom, R is an alkyl group or an aryl group and 1xe2x89xa6nxe2x89xa63. Examples of such an organoaluminium compound are trimethyl aluminium, triethyl aluminium, dimethyl aluminium chloride, diethyl aluminium chloride, diethyl aluminium iodide, diisobutyl aluminium chloride, methyl aluminium dichloride, ethyl aluminium dichloride, ethyl aluminium dibromide, isobutyl aluminium dichloride, ethyl aluminium sesquichloride, dimethyl aluminium methoxide, diethyl aluminium phenoxide, dimethylaluminium hydride and diethyl aluminium hydride.
An external electron donor may also be present during the polymerization of the olefine(s). Examples of possible external electron donors are described above with relation to the execution of step c) in the preparation of the catalyst component as internal electron donors. As external electron donors also organo-silicon compounds can be used. Mixtures of external electron donors can also be used.
Examples of organo-silicon compounds that are suitable as external electron donor are: tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltributoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, diethyldiphenoxysilane, diisopropylsilane, diisobutylsilane, n-propyltrimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, isobutylisopropyldimethoxylsilane, phenyltrimethoxysilane, diphenyldimethoxysilane, trifluoropropylmethyldimethoxysilane, bis(perhydroisoquinolino)dimethoxysilane, dicyclohexyldimethoxysilane, dinorbornyldimethoxysilane, di(n-propyl)dimethoxysilane and di(n-butyl)dimethoxysilane.
Preferably an alkoxysilane is used as the external electron donor during the polymerization.
The molar ratio of the metal in the cocatalyst relative to the Ti during the polymerization may vary from 0.1 to 2000. Preferably this ratio is between 5 and 300. The aluminium/electron donor molar ratio in the polymerization mixture is between 0.1 and 200; preferably between 3 and 100.
The catalyst component of the present invention is suitable for the polymerization of mono- and diolefins containing from 2 to 10 carbon atoms, such as ethylene, propylene, butylene, hexene, octene, butadiene and mixtures thereof. The catalyst component is particularly suitable for the polymerization of propylene and mixtures of propylene and ethylene.
The polymerization can be carried out in the gas phase or in the liquid phase. In the case of polymerization in the liquid phase a dispersing agent is present, such as n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, cyclohexane, benzene, toluene or xylene. Liquid olefine can also be used as a dispersing agent.
The polymerization temperature is usually between 0xc2x0 C. and 120xc2x0 C., preferably it is between 40xc2x0 C. and 100xc2x0 C.
The pressure during the polymerization is normally between 0.1 and 6 MPa. The molecular weight of the polyolefine that is formed during the polymerization can be controlled by adding during the polymerization hydrogen or any other agent known to be suitable for the purpose.
The polymerization can be carried out in continuous mode or batchwise. The polymerization can be carried out in several, successive steps. The polymerization can also be carried out by first effecting the polymerization in the liquid phase and then in the gas phase.
The invention will be further elucidated with examples without being limited thereto, and with the assistance of the accompanying drawings, in which: